Laboratory investigations and descriptive epidemiologic studies suggest a role for dietary fat in the etiology of colon, breast, and prostate cancer. However, many case-control and prospective studies have provided inconsistent results and the benefits to be derived from changes in dietary fat intake are intensely debated. Some of the conflicting data results from major limitations in the methodology used to quantitate human fat intake. Estimates of fat intake from food-frequency questionnaires, food diaries, and diet-interviews are frequently associated with errors of 30% or more. This project will focus upon the development of a simple molecular laboratory test to quantitate dietary fat intake. I will define a set of human genes whose expression is modulated by dietary fat concentration. This will be accomplished through the cloning of human homologues of mouse genes which show increased or decreased activity in response to diets high in fat. Several genes, such as LFG1 (Low Fat Gene 1), have been identified using subtraction hybridization cloning techniques with tissue from mice fed diets varying only in fat concentration. Once the human LFG-1, and additional fat-regulated genes have been sequenced, they will be compared to known DNA sequences in computerized data bases. This will determine: (1) whether we have isolated a novel fat regulated gene, (2) whether the gene has been sequenced but not known to be regulated by fat, or (3) has been sequenced land known to be regulated by diet. We will then develop competitive polymerase chain reaction (PCR) techniques for the precise quantitation of LFG1 expression, and other dietary fat regulated genes, in very small tissue samples such as a blood sample, rectal mucosal biopsy, or fine needle biopsy. Using PCR technology we will characterize the expression of LFG1 and other fat regulated genes in a variety of normal and malignant human cells and tissues including: (1) circulating blood monocytes, (2) biopsy specimens of normal and malignant breast, colon, and prostate, and (3) human cells cultured with differing concentrations of serum lipids. The above studies will provide the data necessary for selecting a panel of genes which can be tested in short term studies in human volunteers consuming diets varying in dietary fat concentration. It is our goal that these techniques will ultimately be utilized as quantitative markers for fat intake in geographic epidemiologic studies, migrant population studies, prospective and case control studies, and as an indicator of compliance with a low fat diet in cancer prevention trials.